Most ( greater than 90%) of the industrial chemical processes are catalytic [J. M. Thomas, W. J. Thomas, Principles and Practice of Heterogeneous Catalysis, VCFL Weinheim, 1997]. Of these, a percentage higher than 75% makes use of heterogeneous catalysts [J. H. Clark, Catalysis of organic Reactions by Supported Inorganic Reagents, VCH, Weinheim, 1994]. Heterogeneous catalysts are widely used in the petrochemical industry in several chemical processes including hydrocarbon cracking (on zeolites), olefin hydrogenations (on precious metals) and stereospecific polymerizations [J. H. Clark, Catalysis of Organic Reactions by Supported Inorganic Reagents, VCH, Weinheim, 1994]. On the other hand, many of the chemical synthesis of interest to the pharmaceutical and secondary chemical industries are liquid-phase homogeneous catalytic or stoichiometric processes [G. Sironi, La Chim. and l""Ind., 79 (1997) 1173-1177; M. Hudlicky oxidations in Organic Chemistry, Acs Monograph, No. 186, 1990]. The interest is high in converting homogeneous processes into efficient and clean heterogeneous catalytic conversions. The oxidation of alcohols to carbonyl derivatives is a typical fine chemical production process in need for such conversion [G. Sironi, La Chim. and l""Ind., 79 (1997) 1173-1177]. Due to the urgent demand of new oxidative technologies mentioned above, very recently Sheldon and colleagues were terming xe2x80x9cphilosophers"" stonesxe2x80x9d efficient heterogeneous catalysts for liquid-phase oxidations in widely known international publication [R. A. Sheldon, m, Wallau, I. W. C. E. Arends, U. Schuchardt, Acc. Chem. Res., 31 (1998) 485-433]. Apart from industrial, large-scale high temperature (600xc2x0 C.) catalytic dehydrogenations (equation 1) and oxidative dehydrogenations (equation 2) carried out on Ag and Cu catalysts [M. Muhler in: Handbook of Heterogeneous Catalysis, VCH, Weinheim, 1997],
R1xe2x80x94CHOHxe2x80x94R2xe2x86x92R1xe2x80x94COxe2x80x94R2+H2xe2x80x83xe2x80x83(1)
R1xe2x80x94CHOHxe2x80x94R2+O2xe2x86x92R1xe2x80x94COxe2x80x94R2+H2Oxe2x80x83xe2x80x83(2)
alcohol oxidations are carried out with stoichiometric amounts of oxidants (periodinanes, Dess-Martin reagent, chromium and manganese salts, mineral acids) or by electrochemical reactions. Environmental, economical and technological reasons make of primary importance the substitution of these homogeneous processes with heterogeneous catalytic oxidations carried out with clean oxidants such as O2, HO2O2 or hypochlorite [J. A. Cusumano, J. Chem. Ed., 72 (1995) 959-964]. In general, however, the selectivity required in fine chemicals production is much higher as compared to that of classical large-scale heterogeneous catalysis.
Traditionally, heterogeneous catalysts are obtained by supporting the active species onto an inert solid of high surface area (silica, celite, carbon, alumina, clays etc.) in order to maximise the dispersion of the active species. The solid carrier can be an inorganic oxide or an organic polymer. Phase separation between the catalytic species and the reagents in the reaction mixture permits the facile separation of the catalyst andxe2x80x94in principlexe2x80x94either to reuse the catalyst in a subsequent reaction or its employment in a continuous process in which the reaction product is separated while the reactant is processed. Typically, heterogeneous catalysts ate prepared by impregnation of the inorganic support with a solution of the active species (i.e. metals ions) or by derivatising the surface of the solid in a heterogeneous reaction between the surface reactive groups (hydroxyl) and an organoderivate of the catalytic molecule.
Few mild catalytic oxidative processes are available. Catalysts of platinum and palladium supported on carbon are used at room temperature for alcohol oxidative dehydrogenation (equation 2) in batch reactors containing a suspension of the catalyst particles in a solution of the alcohol through which air is bubbled. The mild reaction conditions make it possible to oxidise sensitive compounds including carbohydrates [M. Besson, F. Lahmer, P. Gallezot, P. Fuertes, G. Flxc3xa8che, J. Catal, 152 (1995) 116-122] and steroids, [T. Akihisa et al., Bull. Chem. Soc. Jpn. 59 (1986) 680-685), but reaction conditions need to be strictly controlled in order to avoid substrate overoxidation and rapid catalyst deactivation (by metal particles oxidation, sintering etc,). An efficient commercial oxidation catalyst is the inorganic oxide titanium silicalite (TS-1) used with aqueous H2O2 (30% w/w) for the catalytic oxidation of primary and secondary alcohols as described in [R. Murugawel. H. W. Roesky, Angew Chem. Int. Ed. Engl., 36 (1997) 477-479]. Selectivity of TS-1, however, is not high and different oxidisable groups such as double bonds and primary or secondary alcohol groups in a substrate are all rapidly oxidised as well.
There exists high demand of new, selective and efficient catalysts of oxidative processes and intense research efforts are devoted towards this aim both in industrial and in academic laboratories world-wide. Recently for instance, a new aerobic selective oxidative process has been described which uses diazo complexes of Cu (I) supported on K2CO3. Alcohols dissolved in apolar organic solvent can be dehydrogenated into carbonyl compounds by using oxygen contained in air as primary oxidant [I. E. Markxc3x3, P. R. Giles, M. Tsukazaki, S. M. Brown, C. J. Urch, Science, 274 (1996) 2044-2046]. Reactions temperatures employed are high (70-90xc2x0 C.) andxe2x80x94due to low surface area of the inorganic supportxe2x80x94an excess of K2CO3 (2 equiv.) is needed for optimum catalytic activity. The Authors therefore suggest the use of di-t-but-azodicarboxylate (DBAD) as a better primary oxidant affording less carbonate burden (10% equiv.) [I. E. Markxc3x3, P. R. Giles, M. Tsukazaki, S. M. Brown, C. J. Urch, Angew. Chem. Int. Ed. Engl., 36 (1997) 2208-2210]. Another novel catalytic reaction system has been introduced in Japan where alcohols are oxidised with 30% H2O2 in the presence of catalytic tungsten complexes with high turnover numbers [R. Nogori, K. Sato, M. Aoki, J. Takahi, J. Am. Chem. Soc., 119 (1997) 12386-12390].
Higly promising candidates suitable for the preparation of efficient heterogeneous catalysts may originate from stable organic nitroxyl radicals. These are di-tertiary-alkyl nitroxyl radicals (FIG. 1) with A representing a chain of two or three atoms (methylene groups) or a combination of one or two atoms with an oxygen or nitrogen atom as described in International patent application PCT/NL94/00217. Typically, the preferred radicals employed belong to the family of the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO, 1) and its derivatives substituted in position 4 (4-oxo-TEMPO, 2). 
These species are highly efficient and versatile catalysts suitable for highly selective oxidation of hydroxyl containing compounds either to carbonyl or to carboxyl compounds, depending an applied reaction conditions. Their use as catalytic mediators in alcohol oxidations has been recently reviewed in depth in [A. E. J. de Nooy, A. C. Besemer, H. van Bekkum, Synthesis, (1996) 1153-1174]. Reactions can be carried our both at acidic and alkaline pH""s with important difference in the selectivity observed. Furthermore, the oxidation reaction can be performed in different reaction media, i.e. in organic solvent, in biphasic water-organic solvent system and in water. In these catalytic oxidations, the active species (oxidant) is the (cyclic) nitrosonium ion which is generated in situ by adding an active primary oxidant including, among the others, Cu (II), NaOCl, NaOBr, NaBrO2, N2O4, K3Fe(CN)6. It is believed that positive nitrogen of the cyclic nitrosonium ion attacks the alcoholic oxygen, with subsequent hydride abstraction in a bielectronic oxidative step involving carbonyl formation and acid release in the reaction mixture. 
The hydroxylamine formed in the oxidative step disproportionates with the free radical to yield the nitrosonium ion or is directly oxidised with the primary oxidant to nitrosonium ion in a bielectronic reaction. As stated above, several alcoholic substrates can be oxidised at completion with high reaction rate and remarkable selectivity (compatibility with other oxidisable groups) and while alcohol oxidation in organic solvent stops at the first stage yielding a carbonyl compound, in H2O the oxidation proceeds through a second oxidative step to yield a carboxylic acid.
In organic solvent containing up to 5% of H2O air can be used as stoichiometric oxidant by adding a catalytic amount of Cu (I) so that, for instance, alcohols containing highly sensitive heterocyclic substitutes can be selectively oxidised (equation 6) into the corresponding carbonyl compound and no base has to be used to take up the acid formed in the oxidative step (equation 5),
2Cu++O2+2H+xe2x86x922Cu2++2H2Oxe2x80x83xe2x80x83(3)
Cu2++TEMPOxe2x86x92TEMPO+Cu+xe2x80x83xe2x80x83(4)
RCH2OH+TEMPO+xe2x86x92RCHO+H+TEMPO-OHxe2x80x83xe2x80x83(5)
RCH2OH+1/2O2xe2x86x92RCHO+H2Oxe2x80x83xe2x80x83(6).
Remarkably, with the CuCl/O2 system as primary oxidant, oxidation of allylic and benzylic alcohols proceeds smoothly even at xe2x88x9270xc2x0 C. [M. F. Semmelhack, C. R. Shmid, D. A. Cortxc3xa9s, C. S. Chou, J. Am. Chem. Soc., 106 (1984) 3374-3376]. The simplicity and effectiveness of this molecular aerobic oxidation should be compared to Cu (I) mediated aerobic oxidations [L. Prati, N. Ravasio, M. Rossi, La Chim. and L""Ind., 79 (1997) 189-196]. In these latter reactions, including that recently developed by Zeneca [I. E. Markxc3x3, P. R. Giles, M. Tsukazaki, S. M. Brown, C. J. Urch, Science, 274 (1996) 2044-2046] or in enzymatic process recently developed [P. Chaudhuri, M. Hess, U. Flxc3x6rke, K. Wieghardt, Angew. Chem., 110 (1998) 2340-2343], hydrogen transfer takes place between the alcoholic substrate and O2, that are both completed to Cu (I) metal center. On the other hand, in TEMPO mediated oxidations, the oxidant is the cyclic nitrosonium ion and the only function of dissolved catalytic amount of Cu (I) is in forming the oxidant Cu (II) by splitting O2 in a catalytic reaction cycle.
In the carbohydrate industry, oxidation is a useful means to obtain products of high added value starting from low cost, non toxic and readily available materials [K. van der Wiele, Carbohydrates in Europe, 13 (1995) 3]. Mono-oxidised sugars are the products of commercial interest but, due to the chemical similarity of different alcoholic groups in sugars, the selectivity of most chemical oxidants is low. Thus, often protection-deprotection steps of different oxidisable hydroxyls are required before and after the chemical oxidative step, as in the case of the commercial production of ascorbic acid (vitamin C) from a sorbose derivative. Accordingly, the introduction of new selective catalytic processes to substitute the traditional stoichiometric oxidations is the object of intense research efforts. New stable bimetallic (Pdxe2x80x94Bi/C) catalysts have been recently introduced for the preparation of mono-oxidised sugars; the catalyst Palatinose(copyright) (Pt/C) is used in an efficient, continuous catalytic process for the oxidation of D-glucose to D-gluconate. in which air is bubbled in an aqueous glucose solution and the reaction product is separated by electrophoresis while the sugar is continuously processed [M. Kunz et al., German patent DE OS 43 07 388 A1]
In contrast to D-gluconic acid, D-glucuronic acid is nor produced on an industrial scale despite its considerable importance [M. Boiret, A. Marty, J. Chem. Ed., 63 (1986) 1009-1011]. Its synthesis on a small scale is carried out with an enzyme and the price of the resulting compound is high. Moreover, native carbohydrate polymer containing carboxylic group at C-6 (polyuronates) find many commercial applications due to their remarkable properties as complexing agents and for abilities to form gels at low-concentrations (hyaluronanes, pectins, xanthan etc) . A major breakthrough in the commercially relevant field of carbohydrate oxidations occurred therefore with the introduction of the regioselective homogeneous oxidation of carbohydrate primary alcohols into carboxylic acids mediated by nitroxyl radicals as described in PCT/NL94/00217. By using NaOBr as stoichiometric oxidant together with a catalytic amount of the radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) at alkaline pH (10) and low temperature (2xc2x0 C.), sugars protected at the anomeric center are rapidly and selectively converted into respective uronates, 
Due to a cyclic reaction mechanism, this alkaline oxidation method affords the rapid (80 min) regioselective primary alcohols oxidation of soluble polymeric carbohydrates (i.e. starch, inulin, pullulan) affording highly valuable and pure solution of the corresponding polyuronate. The use of NaOBr in place of NaOCl significantly increases the reaction rate. At pH 10 reaction rate is fastest while the non-selective oxidation of sugars by hypohalite has a much lower reaction rate and no side products are detected apart from the uronate. A recent comparative study clearly demonstrated the superiority of glucose oxidation mediated by TEMPO as compared to its oxidative dehydrogenation on Pt/C [K. Li, R. F. Helm, Carbohydr. Res., 273 (1995) 249-255]. Another comparative cost analysis comparing TEMPO (with CuCl/air as stoichiometric oxidant) mediated oxidation with several stoichiometric oxidation protocols including the Swern""s method (DMSO, oxalyl chloride) clearly supports the choice of the former as optimal method for fine alcohol oxidations [K, Dean Bowles, D. A. Quincy, J. I. McKenna, N. R. Natale, J. Chem, Ed., 63 (1986) 358-360]. The analysis took in consideration the expense of solvents and was based on 5 mol % as the amount of free radical needed for obtaining reasonable yields. A further advantage was found in the ease of upscaling of the method. It should be noted that the use of O2 as the primary oxidant (and consequent formation of H2O as unique by-product) along with the low toxicity of the radicals are ideal intrinsic characteristics of the method from both environmental and safety viewpoints.
The versatility of alcohol oxidation mediated by nitroxyl radicals makes their use attractive to diverse industries. Accordingly, several homogeneous oxidative processes mediated by nitroxyl radicals have been patented and are commercially being used for the production of fine chemicals, including high yield (91.6%) E-retinol oxidation to E-retinal with CuCl/O2 in DMF [G. H. Knaus, J. Paust, German.patent 3.705 785], the above mentioned alkaline regioselective oxidation of carbohydrate in water [PCT/NL94/00217], and the oxidation of alkyl polyglucosides (APG""s) and several long chain alcohols (German patent DE 4209 869). Since nitroxyl radicals are costly (xe2x88x9210 S/g on a small scale, Aldrich catalogue 1999) and moderately toxic [T. S. Straub, J. Chem. Ed., 68 (1991) 1048-1049], their recovery would be desirable. Immobilization of the radicals on solid supports would facilitate their separation from the reaction mixture.
Few immobilization procedures have been reported and, with a single exception reported below, all concern organic polymers. A copolymerisation of an organic monomer containing a TEMPO precursor has been described in which the TEMPO precursor fragments are polymerised and then converted to TEMPO fragments [T. Miyazawa, T. Endo, M. Okawara, J. Polym. Sci., Polym. Chem. Ed., 23 (1985) 1527-1535]. Similarly, 4-amino-TEMPO has been immobilized on poly(acrylic acid) and the resulting polymer was subsequently coated on a glassy electrode [T. Osa et al., Chem. Lett., (1988) 1423-1428]. In the carbohydrate field, especially aiming at pharmaceutical and food applications, the preparation of heterogeneous catalysts of immobilisod nitroxyl radicals has been recently attempted. The reductive amination of the keto 4-oxo-TEMPO function by adding its solution in MeOH to a suspension of an amino-silica (Bio Sil NH2 90 15-35, Bio Rad), was followed by a reduction step with NaBH3CN as described in International patent application [PCT/NL96/00201]. As stated in the cited review it remains to be shown that the immobilized radicals are stable after frequent use and longer periods of time [A. E. J. de Nooy, A. C. Besemer, H. van Bekkum, Synthesis, (1996) 1153-1174]. Thus, for instance the catalytic activity of the material thereby obtained was tested in the oxidation of anomerically protected D-glucose; upon 3 consecutive un the material had lost its catalytic properties while reaction rate was considerably lower than corresponding homogenous reaction [A. Heeres, H. van Doren, K. F. Gotlieb, I. P. Bleeker, Carbohydr. Res., 299 (1997) 221-227]. The Authors concluded that azeotropic distillation is the method of choice for the recovery of TEMPO [PCT/NL96/00201].